The present invention relates to a method and a device for trapping ruthenium present in a gaseous effluent. The trapping method of the present invention comprises the use of an aqueous solution or slurry of an alkylene glycol polymer or an alkylene glycol copolymer, in which the alkylene(s) has (have) from 2 to 6 carbon atoms, in order to trap ruthenium present in a gaseous effluent. The ruthenium-trapping cartridge of the present invention has a surface (S) on which an alkylene glycol polymer or an alkylene glycol copolymer is placed, in which the alkylene(s) has (have) from 2 to 6 carbon atoms. The present invention makes it possible in particular both to favour the trapping and the chemical operation of reducing ruthenium oxide RuO.sub.4.